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-   -   Engine runs rough. (http://www.hotrodders.com/forum/engine-runs-rough-69637.html)

lt1bbody 09-06-2005 07:25 PM

Engine runs rough.
 
I have a sb 350 that doesn't seem to idle well like it misses. I recently rebuilt it and it ran great until I blew the trans pump. I replaced it with another tranny and it seem to run fine except for the slip from first to second. The car idles real rough I changed fuel filter, cap, rotor, coil, and even rebuilt the carb. I can chenged idle mixture screws, and timing but niether seem to help at all. When give it more throttle it seems to smooth out some. The car also dies frequently at low rpms under light throttle. I checked the plug wires many of times and they all seem to be fine. What should I check next fuel pump? Ign. module? I'm begining to think this engine is cursed with all the problem I have had with it.

poncho62 09-06-2005 07:30 PM

How old are the plugs.......sometimes, new ones make a world of difference.

Also, how are you checking the plug wires? A visual inspection is not enough.

lt1bbody 09-06-2005 07:34 PM

The plugs have about 50 miles on them since idon't have an DMM right now I can only visually check the wires but they are just as old as the plugs.

scholman 09-06-2005 08:59 PM

It1bbody,

Check the vacuum modulator at the trasmission. The vacuum hose might have fallen off.

Scholman

73oldsman 09-07-2005 06:56 AM

Pop the hood on a dark night and look at the plug wires. Look especially around the plug area to see if sparks are jumping from the wire to the block. Any doubt, replace them.

Velyx21 09-07-2005 11:27 AM

sounds like bad plug wire someewhere, my car had the same symptoms. Popped one of the plug wires and boot was brittle and cracked open, it was arcin to the header.

lt1bbody 09-07-2005 09:51 PM

I just checked the wires doing what 73oldsman said and found it arching to the block on the #2 cylinder. I'll get some new wires for it tomorrow and tell you what happens. I didn't think the wires could be bad since they are new, but from taking them off and on as many times as I did from all the misc. problems I had with the engine: dist 180 off, no oil to left bank (cam bearing problem), I guess the wires get worn out quick. I'm glad that I'm having all these problems now being that it is the first engine I built. It will be easier for me to solve similar problems in the future. Thanks.

lt1bbody 09-08-2005 02:46 PM

I changed to some new wires and now the engine won't even stay running ( i first changed just the #2 cylinder wire then all). I'm thinking there is a problem with the ign. module because it is pretty warm out today and is really sunny causing a lot of heat under the hood. Last night it was running ok and was idling ok even with the #2 cylinder arching. Is there a way I can check the module to see if it is bad?

steve t 09-08-2005 04:15 PM

when a module go bad it want crank, you may have crossed wires

docvette 09-09-2005 03:01 AM

Module
 
Doc here, :pimp:

Pull the module and take it to the local auto parts store..They can test it for you free..

If it is bad ,and you get a new one, Have that one tested too...THE OBF rate on those is about 1 in 3...and once you leave the store it's your problem..make sure they test it several times to heat it up.

When re installing the old one or installing a new one..DON"T FORGET The Silicone heat sink grease..without it you'll be doing it again in a few weeks. Clean all the old stuff off, and generously but not sloppy, apply to the module, and a just a dab to the advance plate.

Make sure module wires aren't shorting to anything and have movement with the advance plate..Inspect the Magnetic pickup while your in there and make sure there are no metal shavings sticking to it.

BAD PLUG WIRES are major contributers to the premature failure of Modules, because they set up a high tension RFI that back feeds into the dizzy and blows the ECM substrate apart...So anymore mis fires are not the only consequence of running with "BAD WIRES" until payday...

Doc :pimp:

lt1bbody 09-09-2005 10:15 AM

I had the module tested and it passed he checked 5 times. Under where the module is there is a white buildup like oxidation can this cause the engine to run rough or not at all? I'm going to check all the wires and connections under the cap, clean off the oxidation, put some new lithium grease under the module and put it back together to see what happens. I'll post once I do this as long as it doesn't rain today.

lt1bbody 09-09-2005 11:53 AM

I cleaned everything real well and checked all the wires. no breaks loose connectors ect. I guess I'm going to buy a new module because I just don't know what else there is to check everything seems to be ok :smash:

Velyx21 09-09-2005 12:25 PM

hmm maybe ur plugs are carboned up really bad.. ??

T-bucket23 09-09-2005 12:51 PM

bad Idle
 
Sounds like a vacuum leak. My guess is you either broke or didnt re-connect the vacuum line to the modulator after the tranny work. have you tried a vacuum gauge to see what it reads. I think you need to start from the begining. If the wires were arcing they are bad or the wrong wires. Make sure you have a good set to start with. I would also replace the plugs, they are fairly cheap and also can not be completly ruled out with just a visual inspection. Assuming the car ran ok before you pulled the tranny, you need to look at what could have happend during that procedure and for gods sakes stop throwing parts at it.
More info would be helpfull also, what year, what tranny etc

T-bucket23 09-09-2005 01:16 PM

Quote:

Originally Posted by lt1bbody
I had the module tested and it passed he checked 5 times. Under where the module is there is a white buildup like oxidation can this cause the engine to run rough or not at all? I'm going to check all the wires and connections under the cap, clean off the oxidation, put some new lithium grease under the module and put it back together to see what happens. I'll post once I do this as long as it doesn't rain today.

That "white build up " is thermal transfer grease and is supposed to be there. It helps to cool the module while still alowing an elecrical connection. If you dont put some on the module and plate you will be replacing the module soon.
Dont use lithium graese, get the proper grease from the parts store or a Radio Shack, either should have it. It usually comes in a little syringe type applicator.


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